Spatio-temporal Variation of Water Heat Flux Using MODIS Land Surface Temperature Product over Hulun Lake, China During 2001–2018

Heat flux is important for studying interactions between atmosphere and lake. The heat exchange between air-water interfaces is one of the important ways to govern the temperature of the water surface. Heat exchange between the air-water interfaces and the surrounding environment is completed by solar radiation, conduction, and evaporation, and all these processes mainly occur at the air-water interface. Hulun Lake was the biggest lake which is also an important link and an indispensable part of the water cycle in Northeast China. This study mapped surface energy budget to better understand spatial and temporal variations in Hulun Lake in China from 2001 to 2018. Descriptive statistics were computed to build a historical time series of mean monthly heat flux at daytime and nighttime from June to September during 2001–2018. Remote sensing estimation methods we used was suitable for Hulun Lake (R2 = 0.81). At month scale, shortwave radiation and latent heat flux were decrease from June to September. However, the maximum sensible heat flux appeared in September. Net longwave radiation was the largest in August. The effective heat budget showed that Hulun Lake gained heat in the frost-free season with highest value in June (686.31 W/m2), and then steadily decreased to September (439.76 W/m2). At annual scale, net longwave radiation, sensible heat flux and latent heat flux all show significant growth trend from 2001 to 2018 (P < 0.01). Wind speed had the well correlation on sensible heat flux and latent heat flux. Water surface temperature showed the highest coefficient in sensitivity analysis.